1. Technical Field
The present invention relates to a hydraulic lash adjuster.
2. Related Art
Japanese Patent Application Publication No. JP-A-2009-191690 discloses a lash adjuster including a bottomed cylindrical body and a bottomed cylindrical plunger which is inserted into the body so as to be reciprocable in an up-down direction. The plunger has an upper end which protrudes out of the body and which is provided with a substantially semispherical support supporting a rocker arm.
A low-pressure chamber is defined inside the plunger, and a high-pressure chamber is located at a lower interior of the body and defined by a bottom wall of the plunger. The bottom wall of the plunger has a valve port extending therethrough. When the valve port is opened, an operating oil (oil) stored in the low-pressure chamber flows through the valve port into the high-pressure chamber. The plunger changes an amount of protrusion out of the body according to a change in an amount of oil filling the high-pressure chamber, so that the rocker arm can be supported by the lash adjuster at a proper heightwise position.
The plunger has a peripheral wall on which an annular band portion is provided so as to extend over an entire circumference of the peripheral wall. The band portion abuts against an upper part of a peripheral wall of the body substantially in a liquid-tight manner. The peripheral wall of the plunger has one inner communication hole (a plunger oil hole) which extends therethrough and is located below the band portion. The band portion prevents oil from flowing out through a gap between both peripheral walls of the plunger and the body and further prevents foreign matter from externally invading the gap. Furthermore, a lower end of the inner communication hole defines a level of the oil stored in the low-pressure chamber.
The lash adjusters have recently had a tendency to be reduced in size with downsizing of engines. Under these circumstances, settings rendering an increase in an inner volume of the low-pressure chamber difficult are sometimes required of the lash adjusters. In this case, the height position of the inner communication hole may be raised if an amount of oil equal to or larger than a current amount is stored in the low-pressure chamber. However, since the band portion is located above the inner communication hole, an amount of raise of the inner communication hole has a definite limitation with a result that a necessary amount of oil cannot sometimes be stored in the low-pressure chamber. In view of the circumstances, it is considered that, for example, an oil level may be raised by reducing a diameter of the inner communication hole so that a lower end of the inner communication hole is located higher. However, when the diameter of the inner communication hole becomes excessively small, a flow rate of oil passing through the inner communication hole is reduced with a result that a sufficient amount of oil cannot sometimes be supplied into the low-pressure chamber.